high intensity interval training hiit

For years the general norm of the fitness world has been that the best method to burn off extra body fat was through the adoption of low-intensity aerobic exercise. New studies have however proven that while you do burn some fat through this method, it is still not the most optimized and most effective method to get the best results from your weight loss efforts.

Majority of these studies have proven that High Intensity Interval Training (HIIT) is a safe and far more effective method to lose extra body fat. High intensity interval training is a specialized form of interval training that involves the combination of short high-intensity exercise intervals with long low-intensity recovery intervals during a workout session. Essentially HIIT involves you doing a number of short burst of intense exercise followed by a longer recovery period without necessarily stopping exercise in between.

The different intensity levels that can be experienced during a workout session are usually determined through a rating system referred to as the Rate of Perceived Exertion (RPE). It is a personalized rating system as it is based on your current fitness level and overall perception of exercise.

On a scale of 1 to 10, with 1 being minimum exertion and 10 being the most intense, the RPE intensity scale would be as follows: a) Low Intensity (1 – 4); b) Moderate Intensity (5-7); and c) High Intensity (8-10).

The true beauty of achieving dramatic weight loss comes from the effect of getting to the last three stages of the RPE scale (8, 9, and 10) – through high intensity. On getting to stage 8 out of 10, the muscles virtually turn to carbohydrates due to the insufficiency of oxygen supply to effectively metabolize its store of triglycerides – fats stored in the muscles. With any further increase in intensity, the muscles will have to completely turn to glycogen – a mixture of glucose and water – as its primary source of energy.

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Stages 9 – 10 of the RPE scale are basically 100% anaerobic stages whereby you are virtually exercising without oxygen. Anaerobic exercises are such that you cannot maintain the state for too long as your muscles soon start to fail. This muscle failure experienced when exercising anaerobically is often attributable to the rapid production of lactic acid which is now building up too rapidly than it is being cleared away from the muscles.

Now, let’s look at what is really happening to better understand why high intensity interval training is such an effective way to lose extra body fat. Let’s call to remembrance the fact that exercising in the low-intensity and moderate intensity "fat burning zones" has what is referred to as a "burn off" effect – the stoppage of fat burning immediately you finish exercising.

The depletion of glycogen due to lack of sufficient oxygen during anaerobic workouts, results in an increase in the production level of lactic acid. The more calories that are burned during anaerobic workouts – by increasing the intensity and duration of the workout – the more glycogen that will be depleted from the muscles resulting in a proportionate increase in the production level of lactic acid.

The true benefits of high intensity workouts are experienced after the workout itself when oxygen becomes readily available again. This is experienced through a process called EPOC – Excess Post-Exercise Oxygen Consumption – which is regarded as the amount of oxygen need by the body to recover from the muscular strain resulting from high intensity workouts.

On the resumption of normal oxygen supply during the recovery phase, about one-fifth of the produced lactic acid in the muscles is oxidized to become carbon dioxide and water. The energy produced by the oxidation (burning) of the lactic acid is then used to turn the remaining lactic acid back to glycogen so the cycle can repeat after recovery when you are resting. Invariably, the more glycogen that is depleted, the more the production of lactic acid and the more additional glycogen that will be produced leading to an increase in lean body mass – increase in low-fat percentage muscle mass.

Also, research has proven that the secretion of human growth hormone is generally increased by exercise, stress and lowered glucose intake amongst other factors. Consequently, the increased lactic acid production which is due to the depletion of glycogen – being a mixture of ‘glucose’ and water – results in a significant boost in human growth hormone secretion.

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In order to get energy fuel to cope with the increased glycogen (carbohydrates) restoration, muscle repairs and muscle growth – triggered by the increase in growth hormone production – the body turns once again to lipolysis (the metabolizing of its stored body fat) as its primary source of energy.

According to several studies, this process of glycogen restoration, muscle repairs and growth fueled by burning of excess body fat continues for more than 24 hours after you have stopped doing high intensity workouts. Some studies assert that the burning of fat can be as much as 105% higher after high-intensity workouts. In another study, almost 16 hours after high intensity workout, there was still a noticeable 63% increase in fat burning.

From all indications, there are noticeably two major factors which can be said to be responsible for the increased fat burning experienced after high intensity workouts. Firstly, there is the increase of two catecholamines – epinephrine (adrenaline) and norepinephrine. Both are generally known to prepare the body for physical exertion by significantly increasing the heart rate, blood pressure and burning of fat depending on the level of threat or intensity of exertion.

Secondly, there is the increased production of human growth hormones spurred by the increased production of lactic acid. Growth hormones are generally regarded as one of the most powerful activator of lipolysis and this greatly contributes to the post-exercise fat oxidation.

In conclusion, high intensity workouts (interval training) results in a significant boost in the body’s fat burning capabilities for more than 24 hours after workout. This is as a result of the excitatory effect of the high intensity workout on some hormones – specifically human growth hormones, epinephrine, and norepinephrine.